Hydra plant. Class Hydrozoa
The common hydra lives in freshwater bodies of water, attaches itself on one side of its body to aquatic plants and underwater objects, leads a sedentary lifestyle, and feeds on small arthropods (daphnia, cyclops, etc.). Hydra is a typical representative of coelenterates and has characteristic features of their structure.
External structure of the hydra
The hydra's body size is about 1 cm, excluding the length of the tentacles. The body has a cylindrical shape. On one side there is mouth opening surrounded by tentacles. On the other side - sole, they attach the animal to objects.
The number of tentacles can vary (from 4 to 12).
Hydra has a single life form polyp(i.e., it does not form colonies, since during asexual reproduction the daughter individuals are completely separated from the mother; hydra also does not form jellyfish). Asexual reproduction occurs budding. At the same time, a new small hydra grows in the lower half of the hydra’s body.
Hydra is capable of changing its body shape within certain limits. It can bend, bend, shorten and lengthen, and extend its tentacles.
Internal structure of the hydra
Like all coelenterates, in terms of the internal structure of the body, the hydra is a two-layer sac that forms a closed structure (there is only a mouth opening) intestinal cavity. The outer layer of cells is called ectoderm, internal - endoderm. Between them there is a gelatinous substance mesoglea, mainly performing a supporting function. The ectoderm and endoderm contain several types of cells.
Mostly in the ectoderm epithelial muscle cells. At the base of these cells (closer to the mesoglea) there are muscle fibers, the contraction and relaxation of which ensures the movement of the hydra.
Hydra has several varieties stinging cells. Most of them are on the tentacles, where they are located in groups (batteries). The stinging cell contains a capsule with a coiled thread. On the surface of the cell, a sensitive hair “looks” out. When the hydra's victims swim by and touch the hairs, a stinging thread shoots out of the cage. In some stinging cells, the threads pierce the arthropod's cover, in others they inject poison inside, in others they stick to the victim.
Among the ectoderm cells, Hydra has nerve cells. Each cell has many processes. Connecting with their help, nerve cells form the hydra nervous system. Such a nervous system is called diffuse. Signals from one cell are transmitted across the network to others. Some processes of nerve cells contact epithelial muscle cells and cause them to contract when necessary.
Hydras have intermediate cells. They give rise to other types of cells, except epithelial-muscular and digestive-muscular. All these cells provide the hydra with a high ability to regenerate, that is, restore lost parts of the body.
In the body of the hydra in the fall they are formed germ cells. Either sperm or eggs develop in the tubercles on her body.
The endoderm consists of digestive muscle and glandular cells.
U digestive muscle cell on the side facing the mesoglea there is a muscle fiber, like epithelial muscle cells. On the other side, facing the intestinal cavity, the cell has flagella (like euglena) and forms pseudopods (like amoeba). The digestive cell scoops up food particles with flagella and captures them with pseudopods. After this, a digestive vacuole is formed inside the cell. The nutrients obtained after digestion are used not only by the cell itself, but are also transported to other types of cells through special tubules.
Glandular cells secrete a digestive secretion into the intestinal cavity, which ensures the breakdown of prey and its partial digestion. In coelenterates, cavity and intracellular digestion are combined.
Movement. Hydra can move from place to place. This movement occurs in different ways: either the hydra, bending in an arc, sticks with the tentacles and partly the glandular cells surrounding the mouth to the substrate and then pulls up the sole, or the hydra seems to “tumble”, attaching itself alternately with the sole and with the tentacles.
Nutrition. The stinging capsules entangle the prey with their threads and paralyze it. The prey processed in this way is captured by the tentacles and directed into the mouth opening. Hydras can “overpower” very large prey that exceeds them in size, for example evenfish fry. The extensibility of their mouth and entire body is great. They are very voracious - one hydra can swallow up to half a dozen daphnia in a short period of time. Swallowed food enters the gastric cavity. Digestion in hydras is apparently combined - intra- and extracellular. Food particles are drawn in by endoderm cells with the help of pseudodopodium inside and are digested there. As a result of digestion, nutrients accumulate in the cells of the endoderm, and grains of excretory products appear there, which are released from time to time in small portions into the gastric cavity. Excretion products, as well as undigested parts of food, are thrown out through the mouth
I - individual with male gonads; II—individual with female gonads
Reproduction. Hydras reproduce asexually and sexually. Etc; Through asexual reproduction, buds are formed on the hydra, which gradually detach from the mother’s body. Budding of hydras under favorable nutritional conditions can occur very intensively; observations show that in 12 days the number of hydras can increase 8 times. During the summer period, hydras usually reproduce by budding, but with the onset of autumn, sexual reproduction begins, and hydras can be both hermaphroditic and dioecious (stalked hydra).
Reproductive products are formed in the ectoderm from interstitial cells. In these places, the ectoderm swells in the form of tubercles, in which either numerous spermatozoa or one amoeboid egg are formed. After fertilization, which occurs on the body of the hydra, the egg cell is covered with a membrane. Such a shell-covered egg overwinters, and in the spring a young hydra emerges from it. There is no larval stage of hydras.
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In the article, readers will be able to find out what hydra is. You will also get acquainted with the history of the discovery, the characteristics of this animal and its habitat.
History of the discovery of the animal
First of all, a scientific definition should be given. Freshwater hydra is a genus of sessile (in lifestyle) coelenterates belonging to the hydroid class. Representatives of this genus live in rivers with relatively slow flows or stagnant bodies of water. They are attached to the soil (bottom) or plants. This is a sedentary single polyp.
The first information about what a hydra is was given by the Dutch scientist, microscope designer Antonie van Leeuwenhoek. He was also the founder of scientific microscopy.
A more detailed description, as well as the processes of nutrition, movement, reproduction and regeneration of the hydra, was revealed by the Swiss scientist Abraham Tremblay. He described his results in the book “Memoirs on the history of a genus of freshwater polyps.”
These discoveries, which became the subject of conversation, brought great fame to the scientist. It is currently believed that it was the experiments in studying the regeneration of the genus that served as the impetus for the emergence of experimental zoology.
Later, Carl Linnaeus gave the genus a scientific name, which came from the ancient Greek myths about the Lernaean Hydra. Perhaps the scientist associated the name of the genus with a mythical creature due to its regenerative abilities: when a hydra’s head was cut off, another grew in its place.
Body structure
Expanding the topic “What is Hydra?”, an external description of the genus should also be given.
The length of the body ranges from one millimeter to two centimeters, and sometimes a little more. The body of the hydra has a cylindrical shape, in front there is a mouth surrounded by tentacles (their number can reach twelve). There is a sole at the back, with the help of which the animal can move and attach to something. There is a narrow pore on it, through which liquid and gas bubbles are released from the intestinal cavity. The individual, together with this bubble, detaches from the support and floats up. In this case, the head is in the water column. In this way, the individual disperses throughout the reservoir.
The structure of the hydra is simple. In other words, the body is a bag whose walls consist of two layers.
Life processes
Speaking about the processes of respiration and excretion, it should be said: both processes occur over the entire surface of the body. Cellular vacuoles play an important role in excretion, the main function of which is osmoregulatory. Its essence lies in the fact that vacuoles remove residual water that enters cells due to one-way diffusion processes.
Thanks to the presence of a nervous system with a mesh structure, the freshwater hydra carries out the simplest reflexes: the animal reacts to temperature, mechanical stimulation, lighting, the presence of chemicals in the aquatic environment and other environmental factors.
Hydra's diet consists of small invertebrates - cyclops, daphnia, oligochaetes. The animal captures prey with the help of tentacles, and the venom of the stinging cell quickly affects it. Then the food is brought by the tentacles to the mouth, which, thanks to body contractions, is, as it were, put on the prey. The hydra throws out the remaining food through its mouth.
Hydra reproduces asexually under favorable conditions. A bud forms on the body of the coelenterate and grows for some time. Later she develops tentacles and also breaks out her mouth. The young individual separates from the mother, attaches to the substrate with tentacles and begins to lead an independent lifestyle.
Hydra sexual reproduction begins in the fall. Gonads are formed on her body, and germ cells are formed in them. Most individuals are dioecious, but hermaphroditism also occurs. Fertilization of the egg occurs in the body of the mother. The formed embryos develop, and in winter the adult dies, and the embryos overwinter at the bottom of the reservoir. During this period they fall into a process of suspended animation. Thus, the development of hydras is direct.
Hydra nervous system
As mentioned above, the hydra has a mesh structure. In one of the layers of the body, nerve cells form the diffuse nervous system. There are not many nerve cells in the other layer. In total, there are about five thousand neurons in the animal’s body. The individual has nerve plexuses on the tentacles, sole and near the mouth. Recent studies have shown that the hydra has a perioral nerve ring very similar to the hydromedusa's nerve ring.
The animal does not have a specific division of neurons into separate groups. One cell perceives irritation and transmits a signal to the muscles. There are chemical and electrical synapses (the point of contact between two neurons) in her nervous system.
Opsin proteins were also found in this primitive animal. There is an assumption that human and hydra opsins have a common origin.
Growth and ability to regenerate
Hydra cells are constantly renewed. They divide in the middle part of the body, then move to the sole and tentacles. This is where they die and flake off. If there is an excess of dividing cells, they move to the kidneys in the lower part of the body.
Hydra has the ability to regenerate. Even after a cross-section of the body into several parts, each of them will be restored to its original form. The tentacles and mouth are restored on the side that was closer to the oral end of the body, and the sole is restored on the other side. The individual is able to recover from small pieces.
Body parts store information about the movement of the body axis in the structure of the actin cytoskeleton. A change in this structure leads to disturbances in the regeneration process: several axes can form.
Lifespan
Speaking about what a hydra is, it is important to talk about the duration of the life cycle of individuals.
Back in the nineteenth century, it was hypothesized that the hydra was immortal. Over the course of the next century, some scientists tried to prove it, and some tried to refute it. Only in 1997 was it finally proven by Daniel Martinez through an experiment that lasted four years. There is also an opinion that the immortality of the hydra is associated with high regeneration. And the fact that adults die in the rivers of the central zone in winter is most likely due to a lack of food or exposure to unfavorable factors.
Hydra biology description internal structure photo lifestyle nutrition reproduction protection from enemies
Latin name Hydrida
To characterize the structure of a hydroid polyp, we can use as an example freshwater hydras, which retain very primitive organizational features.
External and internal structure
Hydras They have an elongated, sac-like body, capable of stretching quite strongly and shrinking almost into a spherical lump. A mouth is placed at one end; this end is called the oral or oral pole. The mouth is located on a small elevation - the oral cone, surrounded by tentacles that can stretch and shorten very strongly. When extended, the tentacles are several times the length of the hydra's body. The number of tentacles varies: there can be from 5 to 8, and some hydras have more. In Hydra, there is a central gastric section, which is somewhat more expanded, turning into a narrowed stalk ending in a sole. With the help of the sole, the hydra attaches to the stems and leaves of aquatic plants. The sole is located at the end of the body, which is called the aboral pole (opposite to the oral, or oral).
The body wall of the hydra consists of two layers of cells - ectoderm and endoderm, separated by a thin basal membrane, and limits a single cavity - the gastric cavity, which opens outwards with the oral opening.
In hydras and other hydroids, the ectoderm is in contact with the endoderm along the very edge of the mouth opening. In freshwater hydras, the gastric cavity continues into the tentacles, which are hollow inside, and their walls are also formed by ectoderm and endoderm.
The ectoderm and endoderm of the hydra consist of a large number of cells of various types. The main mass of cells of both ectoderm and endoderm are epithelial-muscle cells. Their outer cylindrical part is similar to ordinary epithelial cells, and the base adjacent to the basal membrane is elongated fusiform and consists of two contractile muscular processes. In the ectoderm, the contractile muscular processes of these cells are elongated in the direction of the longitudinal axis of the hydra's body. Their contractions cause shortening of the body and tentacles. In the endoderm, the muscular processes are elongated in a circular direction, across the axis of the body. Their contraction has the opposite effect: the body of the hydra and its tentacles narrow and at the same time lengthen. Thus, the muscle fibers of the epithelial-muscle cells of the ectoderm and endoderm, opposite in their action, make up the entire hydra musculature.
Among the epithelial-muscular cells, various stinging cells are located either singly or, more often, in groups. The same type of hydra, as a rule, has several types of stinging cells that perform different functions.
The most interesting are stinging cells with nettle-like properties, called penetrants. When stimulated, these cells release a long filament that pierces the body of the prey. The stinging cells are usually pear-shaped. A stinging capsule is placed inside the cage, covered with a lid on top. The wall of the capsule continues inward, forming a neck, which then passes into a hollow filament, coiled and closed at the end. At the junction of the neck and the filament, there are three spines inside, folded together and forming a stylet. In addition, the neck and stinging thread are lined with small spines on the inside. On the surface of the stinging cell there is a special sensitive hair - the cnidocil, at the slightest irritation of which the stinging thread is ejected. First, the cap opens, the neck is unscrewed, and the stiletto is pierced into the victim’s cover, and the spikes that make up the stiletto move apart and widen the hole. Through this hole, the twisting thread is pierced into the body. Inside the stinging capsule there are substances that have nettle properties and paralyze or kill prey. Once fired, the stinging thread cannot be used again by the hydroid. Such cells usually die and are replaced by new ones.
Another kind of stinging cells of hydras are volventa. They do not have nettle properties, and the threads they throw out serve to hold prey. They wrap around the hairs and bristles of crustaceans, etc. The third group of stinging cells are glutinants. They throw out sticky threads. These cells are important both in retaining prey and in moving the hydra. Stinging cells are usually located, especially on the tentacles, in groups called “batteries”.
The ectoderm contains small undifferentiated cells, the so-called interstitial, through which many types of cells develop, mainly stinging and reproductive cells. Interstitial cells are often located in groups at the base of epithelial muscle cells.
The perception of irritations in hydra is associated with the presence of sensitive cells in the ectoderm that serve as receptors. These are narrow, tall cells with a hair on the outside. Deeper, in the ectoderm, closer to the base of the skin-muscle cells, there are nerve cells equipped with processes through which they contact each other, as well as with receptor cells and contractile fibers of the skin-muscle cells. Nerve cells are located scatteredly in the depths of the ectoderm, forming with their processes a plexus in the form of a mesh, and this plexus is denser on the perioral cone, at the base of the tentacles and on the sole.
The ectoderm also contains glandular cells that secrete adhesive substances. They concentrate on the sole and on the tentacles, helping the hydra temporarily attach to the substrate.
Thus, in the ectoderm of the hydra there are cells of the following types: epithelial-muscular, stinging, interstitial, nervous, sensory, glandular.
The endoderm has less differentiation of cellular elements. If the main functions of the ectoderm are protective and motor, then the main function of the endoderm is digestive. In accordance with this, most of the endoderm cells consist of epithelial-muscle cells. These cells are equipped with 2-5 flagella (usually two), and are also capable of forming pseudopodia on the surface, capturing them, and then digesting food particles. In addition to these cells, the endoderm contains special glandular cells that secrete digestive enzymes. The endoderm also contains nerve and sensory cells, but in much smaller quantities than in the ectoderm.
Thus, the endoderm also contains several types of cells: epithelial-muscular, glandular, nervous, sensory.
Hydras do not remain attached to the substrate all the time; they can move from one place to another in a very unique way. Most often, hydras move “walking”, like the caterpillars of moths: the hydra bends with its oral pole towards the object on which it sits, sticks to it with its tentacles, then the sole comes off the substrate, is pulled up to the oral end and is attached again. Sometimes the hydra, having attached itself to the substrate with tentacles, lifts the stem with the sole upward and immediately carries it to the opposite side, as if “tumbling.”
Hydra Power
Hydras are predators; they sometimes feed on quite large prey: crustaceans, insect larvae, worms, etc. With the help of stinging cells, they capture, paralyze and kill prey. Then the victim is pulled with tentacles to the highly distensible mouth opening and moves into the gastric cavity. In this case, the gastric region of the body becomes greatly inflated.
Digestion of food in hydra, unlike sponges, only partially occurs intracellularly. This is associated with the transition to predation and the capture of fairly large prey. The secretion of glandular cells of the endoderm is secreted into the gastric cavity, under the influence of which the food softens and turns into mush. Small food particles are then captured by the digestive cells of the endoderm, and the digestion process is completed intracellularly. Thus, in hydroids, intracellular or cavity digestion first occurs, which occurs simultaneously with the more primitive intracellular digestion.
Protection from enemies
The nettle cells of the hydra not only infect prey, but also protect the hydra from enemies, causing burns to predators attacking it. And yet there are animals that feed on hydras. These are, for example, some ciliated worms and especially Microstomum lineare, some gastropods (pond worms), Corethra mosquito larvae, etc.
The hydra's ability to regenerate is very high. Experiments carried out by Tremblay back in 1740 showed that pieces of the body of a hydra, cut into several dozen pieces, regenerate into a whole hydra. However, high regenerative ability is characteristic not only of hydras, but also of many other coelenterates.
Reproduction
Hydras reproduce in two ways - asexual and sexual.
Asexual reproduction of hydras occurs by budding. Under natural conditions, hydra budding occurs throughout the summer. In laboratory conditions, budding of hydras is observed with sufficiently intense nutrition and a temperature of 16-20 ° C. Small swellings are formed on the body of the hydra - buds, which are protrusions of the ectoderm and endoderm outward. In them, due to the multiplying cells, further growth of the ectoderm and endoderm occurs. The kidney increases in size, its cavity communicates with the gastric cavity of the mother. At the free, outer end of the bud, tentacles and a mouth opening are finally formed.
Soon the newly formed young hydra separates from the mother.
Sexual reproduction of hydras in nature is usually observed in the fall, and in laboratory conditions it can be observed with insufficient nutrition and a drop in temperature below 15-16 ° C. Some hydras are dioecious (Pelmatohydra oligactis), others are hermaphrodites (Chlorohydra viridissima).
Sex glands - gonads - appear in hydras in the form of tubercles in the ectoderm. In hermaphrodite forms, male and female gonads are formed in different places. The testes develop closer to the oral pole, and the ovaries develop closer to the aboral pole. A large number of motile sperm are formed in the testes. Only one egg matures in the female gonad. In hermaphrodite forms, the maturation of sperm precedes the maturation of eggs, which ensures cross-fertilization and eliminates the possibility of self-fertilization. The eggs are fertilized in the mother's body. The fertilized egg is covered with a shell and spends the winter in this state. Hydras, as a rule, die after the development of sexual products, and in the spring a new generation of hydras emerges from the eggs.
Thus, in freshwater hydras, under natural conditions, there is a seasonal change in forms of reproduction: throughout the summer, hydras bud intensively, and in the fall (for central Russia - in the second half of August), with a decrease in temperature in reservoirs and a decrease in the amount of food, they stop reproducing budding and proceed to sexual reproduction. In winter, hydras die, and only fertilized eggs overwinter, from which young hydras emerge in the spring.
The freshwater polyp Polipodium hydriforme also belongs to the order Hydra. The early stages of development of this polyp take place in the eggs of sterlets and cause them great harm. Several types of hydra are found in our reservoirs: stalked hydra (Pelmatohydra oligactis), common hydra (Hydra vulgaris), green hydra (Chlorohydra viridissima) and some others.
From this article you will learn everything about the structure of freshwater hydra, its lifestyle, nutrition, and reproduction.
External structure of the hydra
Polyp (meaning "multipede") hydra is a tiny translucent creature that lives in the clean, transparent waters of slow-flowing rivers, lakes, and ponds. This coelenterate animal leads a sedentary or sedentary lifestyle. The external structure of freshwater hydra is very simple. The body has an almost regular cylindrical shape. At one of its ends there is a mouth, which is surrounded by a crown of many long thin tentacles (from five to twelve). At the other end of the body there is a sole, with the help of which the animal is able to attach to various objects under water. The body length of freshwater hydra is up to 7 mm, but the tentacles can greatly stretch and reach a length of several centimeters.
Radiation symmetry
Let's take a closer look at the external structure of the hydra. The table will help you remember their purpose.
The body of the hydra, like many other animals leading an attached lifestyle, is characterized by What is it? If you imagine a hydra and draw an imaginary axis along its body, then the animal’s tentacles will diverge from the axis in all directions, like the rays of the sun.
The structure of the hydra's body is dictated by its lifestyle. It attaches itself to an underwater object with its sole, hangs down and begins to sway, exploring the surrounding space with the help of tentacles. The animal is hunting. Since the hydra lies in wait for prey, which can appear from any direction, the symmetrical radial arrangement of the tentacles is optimal.
Intestinal cavity
Let's look at the internal structure of the hydra in more detail. The hydra's body looks like an oblong sac. Its walls consist of two layers of cells, between which there is an intercellular substance (mesoglea). Thus, there is an intestinal (gastric) cavity inside the body. Food enters it through the mouth opening. It is interesting that the hydra, which is not currently eating, has practically no mouth. The ectoderm cells close and grow together in the same way as on the rest of the body surface. Therefore, every time before eating, the hydra has to break through its mouth again.
The structure of the freshwater hydra allows it to change its place of residence. There is a narrow opening on the sole of the animal - the aboral pore. Through it, liquid and a small bubble of gas can be released from the intestinal cavity. With the help of this mechanism, the hydra is able to detach from the substrate and float to the surface of the water. In this simple way, with the help of currents, it spreads throughout the reservoir.
Ectoderm
The internal structure of the hydra is represented by ectoderm and endoderm. The ectoderm is called the body-forming hydra. If you look at an animal under a microscope, you can see that the ectoderm includes several types of cells: stinging, intermediate and epithelial-muscular.
The most numerous group is skin-muscle cells. They touch each other with their sides and form the surface of the animal’s body. Each such cell has a base - a contractile muscle fiber. This mechanism provides the ability to move.
When all fibers contract, the animal’s body contracts, lengthens, and bends. And if the contraction occurs on only one side of the body, then the hydra bends. Thanks to this work of cells, the animal can move in two ways - “tumbling” and “stepping”.
Also in the outer layer are star-shaped nerve cells. They have long processes, with the help of which they come into contact with each other, forming a single network - a nerve plexus that entwines the entire body of the hydra. Nerve cells also connect with skin and muscle cells.
Between the epithelial-muscle cells there are groups of small, round-shaped intermediate cells with large nuclei and a small amount of cytoplasm. If the hydra's body is damaged, the intermediate cells begin to grow and divide. They can turn into any
Stinging cells
The structure of hydra cells is very interesting; the stinging (nettle) cells with which the entire body of the animal, especially the tentacles, are strewn deserve special mention. have a complex structure. In addition to the nucleus and cytoplasm, the cell contains a bubble-shaped stinging chamber, inside which there is a thin stinging thread rolled into a tube.
A sensitive hair emerges from the cell. If prey or an enemy touches this hair, the stinging thread sharply straightens and is thrown out. The sharp tip pierces the victim’s body, and poison flows through the channel running inside the thread, which can kill a small animal.
Typically, many stinging cells are triggered. The hydra grabs prey with its tentacles, pulls it to its mouth and swallows it. The poison secreted by the stinging cells also serves for protection. Larger predators do not touch the painfully stinging hydras. The venom of the hydra is similar in effect to the poison of nettles.
Stinging cells can also be divided into several types. Some threads inject poison, others wrap around the victim, and others stick to it. After triggering, the stinging cell dies, and a new one is formed from the intermediate one.
Endoderm
The structure of hydra also implies the presence of such a structure as the inner layer of cells, endoderm. These cells also have muscle contractile fibers. Their main purpose is to digest food. Endoderm cells secrete digestive juices directly into the intestinal cavity. Under its influence, the prey is split into particles. Some endoderm cells have long flagella that are constantly in motion. Their role is to pull food particles towards the cells, which in turn release pseudopods and capture food.
Digestion continues inside the cell and is therefore called intracellular. Food is processed in vacuoles, and undigested remains are thrown out through the mouth. Breathing and excretion occurs through the entire surface of the body. Let us consider once again the cellular structure of the hydra. The table will help you do this clearly.
Reflexes
The structure of the hydra is such that it is able to sense changes in temperature, the chemical composition of water, as well as touch and other stimuli. The nerve cells of an animal are capable of being excited. For example, if you touch it with the tip of a needle, the signal from the nerve cells that sensed the touch will be transmitted to the rest, and from the nerve cells to the epithelial-muscular cells. The skin-muscle cells will react and contract, the hydra will shrink into a ball.
Such a reaction is bright. It is a complex phenomenon consisting of successive stages - perception of the stimulus, transfer of excitation and response. The structure of the hydra is very simple, therefore the reflexes are monotonous.
Regeneration
The cellular structure of the hydra allows this tiny animal to regenerate. As mentioned above, intermediate cells located on the surface of the body can transform into any other type.
With any damage to the body, the intermediate cells begin to divide, grow very quickly and replace the missing parts. The wound is healing. The regenerative abilities of the hydra are so high that if you cut it in half, one part will grow new tentacles and a mouth, and the other will grow a stem and sole.
Asexual reproduction
Hydra can reproduce both asexually and sexually. Under favorable conditions in the summer, a small tubercle appears on the animal’s body and the wall protrudes. Over time, the tubercle grows and stretches. Tentacles appear at its end and a mouth breaks through.
Thus, a young hydra appears, connected to the mother’s body by a stalk. This process is called budding because it is similar to the development of a new shoot in plants. When a young hydra is ready to live on its own, it buds off. The daughter and mother organisms attach to the substrate with tentacles and stretch in different directions until they separate.
Sexual reproduction
When it starts to get colder and unfavorable conditions are created, the turn of sexual reproduction begins. In the fall, hydras begin to form sex cells, male and female, from the intermediate ones, that is, egg cells and sperm. The egg cells of hydras are similar to amoebas. They are large and strewn with pseudopods. Sperm are similar to the simplest flagellates; they are able to swim with the help of a flagellum and leave the body of the hydra.
After the sperm penetrates the egg cell, their nuclei fuse and fertilization occurs. The pseudopods of the fertilized egg retract, it becomes rounded, and the shell becomes thicker. An egg is formed.
All hydras die in the fall, with the onset of cold weather. The mother's body disintegrates, but the egg remains alive and overwinters. In the spring it begins to actively divide, the cells are arranged in two layers. With the onset of warm weather, the small hydra breaks through the shell of the egg and begins an independent life.